Danon disease: clinical features, evaluation, and management.

Danon disease is an X-linked dominant skeletal and cardiac muscle disorder with multisystem clinical manifestations. It was first described in boys presenting with cardiomyopathy, skeletal myopathy, and varying degrees of intellectual disability.1 As histological findings of glycogen buildup in muscle tissue similar to those seen in Pompe disease were noted, the condition was originally considered to be a lysosomal storage disease and was termed glycogen storage disease type IIb. In 2000, Nishino et al. identified the genetic defects in the lysosome-associated membrane protein 2 (LAMP2) gene, encoding the LAMP2 protein.2 Most Danon disease mutations lead to an absence of LAMP2 protein expression,2 a situation more problematic in males who are hemizygous for LAMP2. For reasons not yet fully understood, reduction in LAMP2 disrupts intracytoplasmic trafficking and leads to accumulation of autophagic material and often glycogen in skeletal muscle and cardiac muscle cells (Figure 1).2 Major clinical features include skeletal and cardiac myopathy, cardiac conduction abnormalities, mild intellectual difficulties, and retinal disease. Males are typically affected earlier and more severely than females. The disease is unfamiliar to many practitioners and the majority of published data stem from case reports with a brief clinical review published in 2002.4 Our aim was to perform a systematic review of Danon disease, provide a comprehensive clinical and molecular update, and propose diagnostic and management guidelines for clinicians and researchers working with Danon disease patients.